This invention relates generally to actuator systems and is concerned more particularly with an efficient fluid actuator system which is responsive to variations in torque output requirements.
Various instances occur in the operation of mechanical equipment where reciprocally movable actuators produce limited angular motion of a rotatable output shaft. Such an arrangement may be used for the operation of aircraft flaps, landing gear, missile fins, rotatable elevational assemblies, earth moving equipment, freight handling equipment and the like.
In one type of actuator system, for example, oil is forced into a cylinder to move a piston and attached rod linearly. The piston rod generally is pivotally connected to an angularly movable moment arm which is attached to a rotatable shaft. Thus, the piston rod acting on the moment arm produces a torque which rotates the output shaft. However, in the described system, the torque developed is a function of the angle of rotation, regardless of the load on the output shaft. Therefore, the energy expended to achieve a particular angle of rotation is proportional to the quantity of fluid required in the hydraulic drive cylinder rather than to the torque required for the load.
Consequently, the described actuator system usually is designed to provide a fluid flow capability which will produce the required torque under maximum load condition. As a result, it will expend the same quantity of energy to achieve a desired angular rotation of the output shaft under minimum load conditions as under maximum load conditions. Thus, if the described actuator system is used to rotate a missile fin, for example, the energy expended to achieve maximum fin angle will be the same when the missile is at extremely high altitudes as when it is at relatively low altitudes where the aerodynamic pressure against the fin is much greater. Also, if the described actuator system is used to rotate the shovel arm of an earth mover, for example, it will expend the same energy to rotate the shovel arm through a particular angle when the shovel is empty as when the shovel is full. Therefore, for efficient operation, the torque developed for rotating the output shaft should be proportional to the load on the shaft.
Thus, there is a definite need for an efficient actuator system of the described type which is responsive to variations in output torque requirements of the system.